Consider 1-bromopropane, CH3CH2CH2Br. (a) Which of these is the lowest energy conformation?

On the following energy diagram, identify the energy level of the cyclohexane conformation shown in the box. Energy (kJ/mol) A) I B) II CLU ||| IV Conformations 2

Q2. Answer any TWO of the following parts: (a) Draw the two main conformations that exist for cyclohexane. Explain clearly why one conformer is more stable than the other. Using cis-1-ethyl-3-methylcyclohexane, as an example, explain how ring flipping occurs. Draw both conformers of cis-1-ethyl-3-methylcyclohexane and explain clearly which one predominates. (b) What is polarimetry? The specific rotation of (R)-carvone is - 61°. A chemist prepared a 750 mg mixture of (R)-carvone and its enantiomer in 10 ml of ethanol and placed the solution in a 10 cm polarimeter cell. The observed rotation was - 4.125°. Calculate the specific rotation for the above mixture. What is meant by enantiomeric excess? Then determine the % enantiomeric excess (% ee) in the mixture. (i) (ii) (iii) What % of the mixture is (R)-carvone and (S)-carvone?

Is there a difference in the stability of the two cyclohexane conformations?

On the more stable conformations (number one part A drawing), can you label each of the carbons as primary, secondary, tertiary, or quaternary.

Which of the following is the most stable conformation of the following compound? II IV III

Problem 3 Propose a reasonable biosynthesis of Fenchone from geranylpyrophosphate (+-Fenchone

Draw the four possible positions, the cis and trans positions of the methyl groups for both the chair and boat conformations, of 1,4-dimethylcyclohexane. Label each as cis or trans and identify the highest in energy.

draw a stable conformation of this compound

Draw all Newman projections of 2,2 bromopropane conformations in which the CH3 group and the H of the CHY2 group are positioned 'gauche' to each other.